1. Field of the Invention
This invention describes a method for treating ocular viral diseases using photodynamic therapy.
2. Prior Art
In order to give a clinical perspective to the significance of viral ocular infections, for example, cytomegalovirus (CMV) retinitis is the most common ocular apportunistic infection and the leading cause of blindness in patients having Acquired Inmune Deficiency Syndrome (AIDS) 30,000 new case being each year in the United States alone. CMV related retinitis has been fond in 30% of AIDS patents, typically late in their diseases processes. The drugs, ganciclovir, and foscarnet, are effective in the treatment of CMV retinitis. With 82%-100% of patents exhibit an initial response to therapy with either drug. All three drugs are virostatic and require daily systemic intravenous administration for the remainder of the patients lives. Such systemic intravenous administration requires the use of an indevelling catheter which has been associated with high rates of infection. In addition all three drugs exhibit various systemic toxicity; with ganciclovir suppressing the bone marrow and both anywhere and foscarnet causing renal toxicity. The use of these compounds for untying ocular retinitisis discussed by Kupparmann, et al. in Ann I Opthalmol, 1993; 115:575-582; and by Holland et al. in Ophthalmol 1987; 94:815-823, and by Caleri et al in Ann. Intern. Med. 1977 126;257-263, A further discussion of the use of theses drugs for treating a retinitis of viral etiology is presented by various AIDS research groups in the New England journal of medicine, 1992; 326; 213-220.
Prior to the advent of antiviral therapy (both anti-CMV and anti-HIV) AIDS patients wit CMV retinitis typically survived only 6 weeks after developing the latter infection. In the current setting of anti-HIV therapy and anti-CMV therapy, median survival has recently been shown to be 8.5 months for patients receiving ganciclovir and 12.6 months for patients receiving foscarnet and more recent studies suggest that median survival is now approaching two years. Longer survival has been associated with greater difficulty related to the continuous suppression of the retinitis over this extended period. Recurrence of the retinitis while on therapy has been reported to occur in 50% of patients within 3 months. (Gross, et al. Ophthalmol. 1990; 97:681-686.) Because of the high incidence of reactivation following the initial favorable response to therapy, the current measure of anti-CMV drug efficacy is based on the length of time to recurrence in addition to the initial therapeutic response to the drug. The fact that the efficacy of anti-CMV agents is, in part, measured by the agents"" ability to prolong the interval for viral reactivation rather than by its ability to effect permanent suppression of viral activity emphasizes the marginal clinical effectiveness of current regimens wherein ganciclovir, acyclovir and foscarnet are administered intravenously. While these three drugs are preventing blindness in most AIDS patients, many patients are still losing their sight. A therapeutic procedure for controlling viral retinitis which reduces systemic toxicity over the current therapies is needed.
The present invention discloses a method for treating ocular viral infections comprising the steps of delivering a phototherapeutic agent to a patient, either systemically or locally, so that the agent accumulates within the infected tissue, followed by light irradiation of the photosensitizer-laden infected tissue. A particular phototherapeutic agent, tin ethyl etiopurpurin (SnET2), shows promise for treating viral ophthalmic diseases. Initial results from preclinical testing with SnET2 and light has demonstrated complete inactivation of cell-free Herpes simplex virus (HSV) and cell associated HSV and CMV in vitro.
It is an object of this invention to provide a method for treating viral associated ocular diseases by means of photodynamic therapy.
It is another object of this invention to provide a treatment for viral associated ocular diseases which has a low toxicity to the patient.
It is still another object of this invention to provide a photosensitizer drug which can be administered to selectively localize and accumulate within infected tissue of the eye and which drug, upon illumination with photoactivating light, provides a therapeutic effect.